From 516af3cb8432fd8fde2b10b8f7e78486d51b69d4 Mon Sep 17 00:00:00 2001
From: Bjarki Arge Andreasen <bjarki@arge-andreasen.me>
Date: Wed, 22 Nov 2023 06:59:44 +0100
Subject: [PATCH] modem: pipe: Add TRANSMIT_IDLE event

Add transmit idle event to modem_pipe_event enum. This will
allow modules to await transmit idle before trying to transmit
more data, instead of blindly calling modem_pipe_transmit in
a loop until all data has been accepted.

This will reduce the time spent trying to transmit data while
the backend is blocked.

Similarly to the RECEIVE_READY event, backends will call
modem_pipe_notify_transmit_idle() to indicate that transmit
is idle, and the TRANSMIT_IDLE event will be reinvoked when
the modem pipe is attached to synchronize the state of the
pipe with the user of it.

Additionally, the TRANSMIT_IDLE event is also invoked when the
modem is opened to further help synchronization with the user
of the pipe.

Signed-off-by: Bjarki Arge Andreasen <bjarki@arge-andreasen.me>
---
 include/zephyr/modem/pipe.h | 13 ++++++++++++-
 subsys/modem/modem_pipe.c   | 21 +++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/include/zephyr/modem/pipe.h b/include/zephyr/modem/pipe.h
index abf8d74918e..a741a94a34c 100644
--- a/include/zephyr/modem/pipe.h
+++ b/include/zephyr/modem/pipe.h
@@ -25,6 +25,7 @@ extern "C" {
 enum modem_pipe_event {
 	MODEM_PIPE_EVENT_OPENED = 0,
 	MODEM_PIPE_EVENT_RECEIVE_READY,
+	MODEM_PIPE_EVENT_TRANSMIT_IDLE,
 	MODEM_PIPE_EVENT_CLOSED,
 };
 
@@ -73,7 +74,8 @@ struct modem_pipe {
 	enum modem_pipe_state state;
 	struct k_mutex lock;
 	struct k_condvar condvar;
-	bool receive_ready_pending;
+	uint8_t receive_ready_pending : 1;
+	uint8_t transmit_idle_pending : 1;
 };
 
 /**
@@ -213,6 +215,15 @@ void modem_pipe_notify_closed(struct modem_pipe *pipe);
  */
 void modem_pipe_notify_receive_ready(struct modem_pipe *pipe);
 
+/**
+ * @brief Notify user of pipe that pipe has no more data to transmit
+ *
+ * @param pipe Pipe instance
+ *
+ * @note Invoked from instance which initialized the pipe instance
+ */
+void modem_pipe_notify_transmit_idle(struct modem_pipe *pipe);
+
 /**
  * @endcond
  */
diff --git a/subsys/modem/modem_pipe.c b/subsys/modem/modem_pipe.c
index 01bdac50d3a..b0088fdefed 100644
--- a/subsys/modem/modem_pipe.c
+++ b/subsys/modem/modem_pipe.c
@@ -21,6 +21,7 @@ void modem_pipe_init(struct modem_pipe *pipe, void *data, struct modem_pipe_api
 	pipe->user_data = NULL;
 	pipe->state = MODEM_PIPE_STATE_CLOSED;
 	pipe->receive_ready_pending = false;
+	pipe->transmit_idle_pending = true;
 
 	k_mutex_init(&pipe->lock);
 	k_condvar_init(&pipe->condvar);
@@ -82,6 +83,10 @@ void modem_pipe_attach(struct modem_pipe *pipe, modem_pipe_api_callback callback
 		pipe->callback(pipe, MODEM_PIPE_EVENT_RECEIVE_READY, pipe->user_data);
 	}
 
+	if (pipe->transmit_idle_pending && (pipe->callback != NULL)) {
+		pipe->callback(pipe, MODEM_PIPE_EVENT_TRANSMIT_IDLE, pipe->user_data);
+	}
+
 	k_mutex_unlock(&pipe->lock);
 }
 
@@ -97,6 +102,7 @@ int modem_pipe_transmit(struct modem_pipe *pipe, const uint8_t *buf, size_t size
 	}
 
 	ret = pipe->api->transmit(pipe->data, buf, size);
+	pipe->transmit_idle_pending = false;
 	k_mutex_unlock(&pipe->lock);
 	return ret;
 }
@@ -179,6 +185,7 @@ void modem_pipe_notify_opened(struct modem_pipe *pipe)
 
 	if (pipe->callback != NULL) {
 		pipe->callback(pipe, MODEM_PIPE_EVENT_OPENED, pipe->user_data);
+		pipe->callback(pipe, MODEM_PIPE_EVENT_TRANSMIT_IDLE, pipe->user_data);
 	}
 
 	k_condvar_signal(&pipe->condvar);
@@ -190,6 +197,7 @@ void modem_pipe_notify_closed(struct modem_pipe *pipe)
 	k_mutex_lock(&pipe->lock, K_FOREVER);
 	pipe->state = MODEM_PIPE_STATE_CLOSED;
 	pipe->receive_ready_pending = false;
+	pipe->transmit_idle_pending = true;
 
 	if (pipe->callback != NULL) {
 		pipe->callback(pipe, MODEM_PIPE_EVENT_CLOSED, pipe->user_data);
@@ -211,3 +219,16 @@ void modem_pipe_notify_receive_ready(struct modem_pipe *pipe)
 
 	k_mutex_unlock(&pipe->lock);
 }
+
+void modem_pipe_notify_transmit_idle(struct modem_pipe *pipe)
+{
+	k_mutex_lock(&pipe->lock, K_FOREVER);
+
+	pipe->transmit_idle_pending = true;
+
+	if (pipe->callback != NULL) {
+		pipe->callback(pipe, MODEM_PIPE_EVENT_TRANSMIT_IDLE, pipe->user_data);
+	}
+
+	k_mutex_unlock(&pipe->lock);
+}